Progressive glomerular and tubular damage in sickle cell trait and sickle cell anemia mouse models

Abstract

Homozygosity for the hemoglobin (Hb) S mutation (HbSS, sickle cell anemia) results in hemoglobin polymerization under hypoxic conditions leading to vaso-occlusion and hemolysis. Sickle cell anemia affects 1:500 African Americans and is a strong risk factor for kidney disease, although the mechanisms are not well understood. Heterozygous inheritance (HbAS; sickle cell trait) affects 1:10 African Americans and is associated with an increased risk for kidney disease in some reports. Using transgenic sickle mice, we investigated the histopathologic, ultrastructural, and gene expression differences with the HbS mutation. Consistent with progressive glomerular damage, we observed progressively greater urine protein concentrations (P = 0.03), glomerular hypertrophy (P = 0.002), and glomerular cellularity (P = 0.01) in HbAA, HbAS, and HbSS mice, respectively. Ultrastructural studies demonstrated progressive podocyte foot process effacement, glomerular basement membrane thickening with reduplication, and tubular villous atrophy with the HbS mutation. Gene expression studies highlighted the differential expression of several genes involved in prostaglandin metabolism (AKR1C18), heme and iron metabolism (HbA-A2, HMOX1, SCL25A37), electrolyte balance (SLC4A1, AQP6), immunity (RSAD2, C3, UBE2O), fatty acid metabolism (FASN), hypoxia hall-mark genes (GCK, SDC3, VEGFA, ETS1, CP, BCL2), as well as genes implicated in other forms of kidney disease (PODXL, ELMO1, FRMD3, MYH9, APOA1). Pathway analysis highlighted increased gene enrichment in focal adhesion, extracellular matrix-receptor interaction, and axon guidance pathways. In summary, using transgenic sickle mice, we observed that inheritance of the HbS mutation is associated with glomerular and tubular damage and identified several candidate genes and pathways for future investigation in sickle cell trait and sickle cell anemia-related kidney disease.

Figure 1

Blood count parameters.

Figure 2

Urine protein concentrations.

Figure 3. Histopathology of the kidney

(original magnification 400x). 3A, 3D and 3G: H & E stained sections; 3B, 3E and 3H: Masson trichrome stained sections; 3C, 3F and 3I: Periodic acid-Schiff stained sections. 3A–C: Glomeruli from Hb AA mouse with normal cellularity and unremarkable tubules. 3D–F: Glomeruli from Hb AS mouse with mild focal segmental mesangial hypercellularity (>) and segmental congestion of glomerular capillary loops (→). 3G–I: Glomeruli from Hb SS mouse with global diffuse mesangial hypercellularity (>) and segmental congestion of glomerular capillary loops (→). 3I: Hb SS mouse with tubular and parietal epithelial deposition of cytoplasmic hemosiderin pigment (*).

Figure 4

(A) Glomerular hypertrophy and (B) cellularity in Hb AA, Hb AS, and Hb SS mice.

Figure 4

(A) Glomerular hypertrophy and (B) cellularity in Hb AA, Hb AS, and Hb SS mice.

Figure 5

5A, 5C and 5E: Ultrastructure of glomeruli, 5B, 5D and 5F Ultrastructure of proximal convoluted tubules. 5A: Hb AA mouse: Glomerular basement membranes are overall fairly uniform in thickness with mainly intact foot processes ( < ). 5B. Hb AA mouse: Tubular basement membranes are overall fairly uniform in thickness with mainly intact brush borders (*). 5C AS: Glomerular basement membranes are variably thickened with focal effacement of foot processes (*). Both examined glomeruli have segmental subendothelial widening and one has early basement membrane reduplication with mesangial interposition (blue arrow). 5D. Hb AS: Tubular brush borders have focal microvillous blunting and shortening (*). 5E. Hb SS: Glomerular basement membranes are variably thickened with focal effacement of foot processes (*). Both examined glomeruli have segmental subendothelial widening and early basement membrane reduplication with mesangial interposition (blue arrow). 5F. SS: Tubular brush borders have focal marked attenuation with pronounced microvillous blunting (*).